The present invention relates to a yarn piecing and knotting device to be used when a yarn breakage takes place in a so-called pneumatic spinning process as disclosed in U.S. Pat. No. 3,079,746 or U.S. Pat. No. 3,978,648 in which a sliver is spun into a yarn by passing the sliver through an air jetting nozzle and false-twisting it by a swirling stream of air jetted from the air jetting nozzle.
In the pneumatic spinning process as described above, since spinning cannot be interrupted even during the yarn knotting operation, a conventional yarn piecing device as customarily used for a winder or the like cannot be directly used as the yarn piecing up means.
As the known means for performing the yarn piecing-up operation without interruption of spinning, there is known a device disclosed in British Pat. No. 1,357,422.
This yarn piecing and knotting device is for use in a so-called open-end spinning process using a rotary rotor. More specifically, a yarn continuously spun by the rotary rotor is caught by a suction pipe and knotted to the end of a yarn on a winding package by a knotter, and the yarn excessively spun during a period ranging from the point of completion of the operation of the knotter to the point of resumption of the winding operation is temporarily retained on a metal net by sucking and attracting the yarn onto the metal wire and on resumption of the winding operation the winding package is rotated at a high speed to wind the excessively spun yarn retained on the metal net onto the winding package. As is well known in the art, in the open-end spinning process, the spinning speed is 60 m/min at highest and hence, the length of the yarn retained on the metal net is extremely short. Accordingly, the yarn knotting operation can be accomplished sufficiently by the above-mentioned yarn knotting mechanism. However, in case of the pneumatic spinning process, the spinning speed is as high as 150 to 250 m/min, and at such high spinning speed the excessively spun yarn is as long as 10 to 30 cm even if the yarn knotter is operated at a speed as high as possible. Accordingly, when the above-mentioned yarn piecing and knotting mechanism is used in the pneumatic spinning process, the excessively spun yarn is deposited and accumulated in the folded state on the metal net. Such defects as entanglements, and loops are thus formed on the yarn, and a kinky thread is produced. If loops and kinks are once formed, they cannot easily be eliminated by pulling the yarn, and the resulting yarn has a fatal defect in quality.
Such excessively spun yarn can be temporarily retained by using a wire instead of the above-mentioned metal net-equipped suction pipe and bending the yarn by this wire. Since the residual torque in a yarn obtained by the pneumatic spinning process is high and kinky threads are readily formed, when the bending is released after resumption of the winding operation, if the rate of release of the bending is higher than the yarn take-up rate of the winding package only a bit, the yarn is slackened and kinky threads are immediately formed. Accordingly, this method is defective in that adjustment of the release of the bending is very difficult.